Power supply for arc-lamp including automatic starting circuit



May 10, 1966 c. E. EVEREST 3,250,953

POWER SUPPLY FOR ARC-LAMP INCLUDING AUTOMATIC STARTING CIRCUIT FiledJuly 6, 1962 2 Sheets-Sheet 1 LM/i/ 1 NVEN TOR. Czar/ 155 A. 0mm)" May10, 1966 C. E. EVEREST POWER SUPPLY FOR ARC-LAMP INCLUDING AUTOMATICSTARTING CIRCUIT Filed July 6, 1962 2 Sheets-Sheet 2 g 11 L /4'0 1F .7 Z

536 4/ a? 1 55 a: m

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J an /7 1 544 INVENTOR. CM a [s5 [l/[AA'57' 3,250,953 POWER SUPPLY FORARC-LAMP INCLUDING AUTOMATIC STARTING CIRCUIT Charles E. Everest, SierraMadre, Calif., assignor to Consolidated Electrodynamics Corporation,Pasadena,

Calif., a corporation of California Filed July 6, 1962, Ser. No. 208,03910 Claims. (Cl. 315200) This invention relates to power supplies for arelamps and more particularly to a power supply for a compactarc lampincorporating an automatic lamp starting circuit.

It is well known that arc lamps produce illumination 'as a result of theproduction of an electrical discharge between a pair of electrodes. Arclamps are available which produce illumination in various portions ofthe spectrum in accordance with the gaseous atmosphere and the gaspressure in which the electrical discharge is produced. Examples of ahigh power are lamp productive of high light intensities in the visiblespectrum are the common carbon arc and mercury vapor lamps that havebeen employed for street lighting purposes. Arc lamps have also beendeveloped that are small and compact that produce extremely highbrightness in the ultraviolet, visible, and infrared regions of thespectrum for special purposes such as microphotography,spectrophotography, direct wire oscillography, and the like. Lamps ofthis type may employ xenon or mercury vapor enclosed in an envelope atrelatively high pressures. The xenon or mercury vapor arc lamps havefound extensive use in present day recording oscillographs and are knownin the art as compact-arc lamps.

As in any are lamp, the compact-arc lamp requires that the electricaldischarge be initiated between the electrodes and then the dischargesustained in order to produce the desired illumination. In thecompact-arc lamp the starting of the lamp or the initiation of theelectrical discharge usually requires the momentary application of avery high voltage pulse in the radio or microwave frequency range. Forexample, a xenon compact-arc lamp may require 10 watts of power on theorder of 15,000 to 30,000 volts in the 1 to '10 megacycle range. Sincethe energization of a compact-arc lamp is sustained in terms ofrelatively low direct current voltages, it will be noted that therequirements for s-tarting'and maintaining the lamp energized areradically different. Accordingly, in many applications and, inparticular the oscillographic applications utilizing the compact-arclamp, separate circuits are utilized for starting the lamp and formaintaining itenergized. It is also characteristic of the startingcircuits that they include relatively complex transistor and relaycircuits for generating a starting pulse and transferring the startingpulse to the arc lamp and then further switching means to transfer thelamp from the switching circuit to the power or energizing circuit. Thishas involved a large number of electrical components that have had alimited life and are sensitive to high voltages and the like. Theseprior art starting circuits furthermore have not been self-starting andgenerally require that a starting button be actuated in order to producethe starting pulse after the power is applied to the lamp. From thestandpoint of the power excitation circuit, the manufacturersspecifications for operating the compact-arc lamps over their rated liferequire that the voltage applied thereto be within certain limits. Toreduce the number of components and expense required for this purpose,some oscillographs employing compact-arc lamps have utilized a manualmeans for regulating the voltage to transfer this function to theoperator rather than incorporating regulating means into the electricalpower circuitry.

United States Patent The present invention provides an improved, simple,small, and relatively inexpensive power supply circuit for are lampsthat incorporates an automatic lamp starting circuit that causes thelamp to be rapidly started. The power supply of the present inventionincludes a minimum of highly reliable electrical components-employs norelays, transistors, moving parts, or the like that have a limitedlife-and which power supply automatically adjusts itself to the aging ofthe lamp. The automatic starting circuit is incorporated into the powertransformer for the lamp and which power transformer is a constantvoltage or regulating transformer that automatically produces voltageregulation on the order of il% of the lamp power. The power supplycircuit arrangement is such that the initiation of the electricaldischarge in the arc lamp is not only automatically started, withoutresorting to any starting buttons, upon the application of power to thesupply circuit but is also advantageously defined whereby the startingcircuits and the lamp energizing circuits 'are essentially independentlyand alternately energized and de-energized in the correct time sequence.Furthermore, upon the loss of power or a sudden drop in power linevoltage below the sustaining voltage of the arc lamp causing it'tobecome de-energized, the starting and energization cycle will be quicklyrepeated whereby the lamp will be automatically ignited within 17milliseconds.

From a structural standpoint the invention comprises a power regulatingtransformer having a magnetic shunt between the primary and secondarywindings for defining a high leakage reactance and which leakagereactance is defined in accordance with the operating characteristics ofthe arc lamp to act as the lamp ballast impedance. The power transformerprimary winding includes a circuit adapted to resonate at the powerfrequency applied thereto and in combination with the saturable coredevelops a substantially constant voltage at the secondary windingmeans. The secondary winding means include a plurality of secondarywindings, one of which is included in the automatic starting circuitWhile the other is included in the energization circuit for the arclamp. The automatic starting circuit is adapted for momentarilygenerating a high frequency, high voltage starting pulse in response tothe energy in its associated secondary winding and proportioned to startthe arc lamp. This starting circuit includes a pair of spaced electrodesfor producing the starting pulse by means of an electrical dischargetherebetween and means for coupling the starting pulse to the arc lampthrough the energizing circuit. The lamp energizing circuit is arrangedwith the other secondary winding and includes rectifying-filter meansfor producing the direct current potential for maintaining the lampenergized. A temporary storage device incorporated in therectifying-filter means is arranged to temporarily store the energyreceived from the primary winding whereby it is effective to unload thissecondary winding or block the transfer of energy thereto and therebycausethe transformer energy to be essentially coupled across thesecondary winding for the starting circuit leading to the production ofthe electrical discharge between the spaced electrodes in the startingcircuit. Upon the production of the electrical discharge in the startingcircuit, the resulting starting pulse is immediately coupled to the arclamp to initiate the electrical discharge for starting the lamp.-Substantially simultaneously with the energization of the lamp, thetemporary storage device is discharged to a voltage level where itunblocks the associated secondary winding and once again is responsiveto the transformer energy to allow the resulting rectified current to beapplied to the arc lamp for maintaining it continuously energized. Withthe application of the energy of the primary winding to the energizingcircuit,

the potential developed at the secondary winding for thestartingycircuit is maintained at a level to prevent a furtherelectrical discharge in the starting circuit and, therefore, essentiallyall of the power from the transformer is transferred to the energizingcircuit to thereby maintain the lamp energized.

These and other features of the present invention may be more fullyappreciated when considered in the light of the following specificationand drawings, in which:

FIG. 1 is a schematic circuit representation of the power supplyincorporating the automatic starting circuit embodying the invention;

FIG. 2 is a diagrammatic representation of the mag netic coreconfiguration for the power transformer of FIG. 1;

FIG. 3 is a schematic illustration of another embodiment of the powersupply circuit of FIG. 1; and

FIG. 4 is a diagrammatic representation of the magnetic coreconfiguration for the power transformer as utilized in the circuit ofFIG. 3.

Now referring to the drawings, the invention will be described as thepower supply circuit may be employed with a compact-mercury arc lamp,although it should be understood that the invention could be used withother types of arc lamps.

The power circuit 10, shown in FIG. .1 comprises a power transformer 11having a plurality of secondary windings 12 and 13. The secondarywinding 12 is included in an automatic lamp starting circuit, while thesecondary winding 13 is included in a lamp power or energizing circuit.A

The power transformer 11 is further characterized as having a highleakage reactance to function as the ballast for the arc lamp 14 shownin circuit relationship with the secondary winding 13. The leakagereactance for the power transformer 11 is defined through the provisionof a magnetic shunt arranged between the primary and secondary windingstherefor, as will be explained more fully immediately hereinafter. Inaddition, the power transformer 11 includes a circuit in combinationwith the primary windings that is resonant to the power frequencyapplied to the primary winding for regulating the supply voltage withinil% for supply voltage changes of 110% or more and, therefore, producesan essentially constant voltage output.

The power transformer 11 is shown as a ferromagnetic transformer havinga center tapped primary winding 15. The primary winding 15 is connectedat its center tap to an inductor 16 connected in series circuittherewith. The inductor 16, as represented in FIG. 1, has an iron core16 including an air gap G arranged in the flux path of the windingtherefor. The air gap G is represented in FIG. 1 as a pair of series ofspaced horizontal lines arranged on opposite sides of the transformercore and identified by the reference letter 6;. The primary winding 15is connected in parallel circuit relationship with a resonatingcapacitor 17 coupled between the opposite ends of the winding 15. Thecapacitor 17 is defined to resonate with the winding 15 at the powerfrequency applied to the primary winding from a suitable source. Ingeneral, the power transformer will be applied to a commercial source ofalternating current and, therefore, the alternating current will be onthe order of 60 cycles and 117 volts. It should therefore be noted thatthe parameters of the primary winding 15 and the capacitor 17 aredefined in terms of this commercial 60 cycle source as Well as the othercomponents to be described hereinafter. The primary' winding 15 is alsoshown arranged with an air gap G for controllably defining the highleakage reactance of the power transformer 11 or controlling thereluctance of the magnetic shunt between the primary winding 15 and thesecondary windings 12 and 13.

Now referring to FIG. 2, the physical configuration of the powertransformer 11 along with the inductor 16 will be more closely examined.It should be noted, at the outset, that the inductor 16 and the powertransformer 11 are shown as separate elements for the purposes of thisinvention but the inductor 16 may readily be incorporated into themagnetic structure for the power transformer 11 to provide a unitaryassembly. The inductor 16 may be constructed in terms of conventionalE-I core laminations with the winding 16 arranged in the central portionof the E lamination, as shown, whereby a closed magnetic flux path isdefined and the air gap G is defined in this flux path between the E andI laminations at the outer legs and is proportioned to cause theinductor to exhibit a linear reactance. The one output terminal from theinductor 16 is connected to the power source while the other terminal isconnected to the center tap of the primary winding 15 for the powertransformer 11, as described hereinafter.

The power transformer 11 is shown as comprising a rectangular core thatmay consist of a pair of E laminations associated with an I laminationdefining a closed flux path. The pair of E laminations 20 and 21 arearranged back to back with the I lamination 22, abutting the Elamination 20 for closing the magnetic flux path. The primary winding 15is arranged on the central arm of the lamination 20, while the secondarywindings 12 and 13 are tightly coupled to the central arm of thelamination 21 whereby voltages induced therein' from one to the otherare constrained to be very nearly their turns ratio.

The primary winding 15 and the secondary windings 12 and 13 are spacedapart in accordance with this construction rather than being tightlycoupled to one another as in conventional transformer design forminimizing the leakage reactance. It will be noted that the portion ofthe magnetic core identified by the reference numeral 20 functions as amagnetic shunt for the flux provided by the primary winding 15 and,therefore, since this flux does not couple the secondary windings 12 and13, may be termed leakage flux. This magnetic shunt is defined inaccordance with thev lamp characteristic whereby the resulting leakagereactance may function as the ballast impedance for the arc lamp 14. Tothis end, this leakage reactance is controlled in accordance with thenecessary operating characteristics of the arc lamp 14 by defining thelength of the air gaps G shown in the shunt arm 2t) on opposite sides ofthe secondary winding 15. Since a compact-arc lamp is generallyconsidered to be a constant power device, this leakage reactance voltageand current characteristic should be defined toward this end.

Now returning to FIG. 1 the circuits associated with the secondarywindings 12 and '13 will be more closely examined. The circuitassociated with the secondary winding 12 is the automatic star-tingcircuit and includes means for generating the high voltage, highfrequency starting pulse for the arc lamp 14. To this end, the startingpulse generating means is shown as a pair of spaced electrodes 25 and 26mounted on an insulating supporting member 27, shown as a U-shapedmember. The electrodes 25 and 26 may be conveniently and inexpensivelyconstructed of a pair of conventional screws threaded into theinsulating member 27 and spaced by an air gap 28 whereby the air gap 28ends may be readily adjusted. As shown, the electrode 26 is connected toa point of reference potential or ground while the electrode 25 isconnected to a starting pulse coupling element shown as a pulsetransformer 31. The primary winding 32 of the pulse transformer 31 isconnected between the electrode 25 and one terminal of the secondarywinding 12 and which secondary winding has its other terminal connectedto ground or in common with the electrode 26.

The other secondary winding 13 .for the power transformer 1 1 is shownconnected to a rectifier-filter combination for producing the directcurrent potential necessary for powering the :arc lamp '14. The circuitelements comprising the rectifier-filtercombinaton are arranged withinthe box shown in dotted outline and comprise a conventional full-wavediode rectifying circuit shown in terms of the semi-conductor dioderectifiers 33 and 34 connected in rectifying relationship to theopposite terminals of the secondary winding 13. The filtering elementassociated with the rectifier is shown in terms of a single zfilteringcapacitor 35 connected in common with the cathodes of the diodes 33 and34 and ground and, accordingly, is common with the grounded center tapfor the secondary winding 13. The energizing circuit is completed bymeans of a circuit connection to the secondary winding 36 for the pulsetransformer 31, which is connected to the anode 14 of the arc lamp 14and which arc lamp has its cathode electrode 14 connected to ground. Thecircuit is further represented as including a resistance element 37connected in series circuit relationship between the capacitor 35 andthe secondary winding 36 of the pulse transformer 31 and includesashorting switch 38 arranged in parallel circuit relationship therewith.The switch 38 is normally closed and, therefore, the resistor 37 can bedisregarded for the purposes of the present discussion.

With the above structure in mind, an examination of the components ofthe circuit of FIG. 1 will make the circuit operation more evident.First examining the power transformer 11 and, in particular, the primarywinding means therefor, it will be noted that the arrangement is suchthat the combination of the resonant circuit comprising the winding andthe capacitor 17 and the magnetic characteristics of its associatedmagnetic core is such that the. portion of the magnetic core associatedwith the primary winding 15 is driven and operated in a saturatedcondition. Therefore, when the primary circuit is operated in saturationa nearly constant rate of change of [flux or constant dqs/dt isestablished in the portion of the core associated with the secondarywindings 12 and 13. This constant rate of change of flux in the portionof the core associated with the secondary circuits occurs during each ofthe half cycles of the. alternating current input signal. It will beappreciated that with a constant rate of change of the flux cutting thesecondary windings 12 and 13 that a nearly square wave output is derivedfrom these windings and an essentially constant amplitude voltage isderived therefrom. The leakage flux that passes through the core portionhas been defined by means of high reluctance elements for the air gaps Gto be consistent with the open circuit voltage and short circuitcurrents of the arc lamp. In addition, the resulting impedancecorresponding to the leakage flux is proportioned to function as aballast impedance to place the load on the arc lamp 14 at the correctvoltage and current for sustaining the energization of the lamp over itsnormal operating range. Specifically, the resulting load characteristicfor the lamp should be adjusted by means of the leakage reactance toallow the voltage and the cur-rent applied to the arc lamp to maintainthe lamp at its rated constant power characteristic.

Now referring to the operation of the starting circuit for the lamp andwhich starting circuit is associated with the secondary winding 12, itwill be seen that normally no current is drawn in this circuit due tothe air gap 28 defined between the electrodes and 26 for generating thestarting pulse. Accordingly, the voltage required to produce anelectrical discharge between the electrodes 25 and 26 may be consideredas the critical voltage required for energizing the starting circuit.This critical voltage necessarily must be defined and proportioned interms of the starting pulse required for the particular are lamp 14utilized in the circuit. In addition, the power circuit or the lowvoltage circuit may be considered to have a critical voltage which isthe open circuit direct current voltage presented to the lamp uponstarting. In a typical compact-mercury arc, 10 watt lamp this opencircuit voltage may be on the order of 55 volts and the open circuitvoltage must be limited to this value. In

practice, this critical low voltage 'value may be obtained by merelyadjusting the length of the air gap 28 between the electrodes 25 and 26until an electrical discharge is produced. To this end, the voltagerequired to cause an electrical discharge between these electrodes orthe voltage V may be defined by the following formula:

wherein N and N refer to the number of turns in the secondary windings12 and 13; (since only one-half of the secondary winding 13 is utilizedduring each half cycle, the formula takes this int-o consideration bythe constant 2.) an E is the rated open circuit voltage for the arclamp.

It should be recognized that the relative setting of the electrodes 25and 26 may be readily attained by moving one electrode towards the otherwhile observing the arc lamp and noting when the lamp is ignited. This,then, sets the pulse generating means to the correct spacing forbreaking down the air to generate the starting pulse and also determinesthe open circuit voltage applied to the lamp 14. It should be recognizedthat an electrical discharge produced between a pair of electrodes isrich in high frequency components and which components are in the rangerequired for triggering a compact-arc lamp. The voltage required forbreaking down the gap and producing the discharge between the electrodes25 and 26 is derived from the secondary winding 12 of the powertransformer 11 and coupled to the lamp 14 by means of the pulsetransformer 31. If the high voltage pulse derived from the secondarywinding 12 is not sufficient, it may be increased by constructing thepulse transformer 13 as a step-up transformer whereby the winding turnsare proportioned to step-up the discharge voltage to the correctrequired starting voltage.

With the above considerations in mind, the operation of the automaticstarting circuit along with the automatic switching of the energy fromthe power transformer primary between the windings 12 and 13 will beexamined in greater detail. When the power is first applied to theprimary winding 15 of the power transformer 11, the loading effect ofthe filter capacitor 35 on the secondary winding 13, plus the currentlimiting elfect of the leakage inductance due to the air gaps G combineto keep the voltages on the tightly coupled secondaries 12 and 13 lowfor a few cycles until the capacitor 35 charges up. As the capacitor 35approaches the open circuit voltage for the lamp 14, or 55 volts, thevoltage between the electrodes 25. and 26 approaches the break downpotential. As the first peak of the input wave exceeds the breakdownvoltage for the electrodes 25 and 26 it results in an electricaldischarge therebetween and the impedance between these electrodesinstantaneously drops to a very low value, as is characteristic of agaseous discharge. Under these conditions the secondary winding 12 iseffectively shorted out and its voltage drops to a very low value. Dueto the tight coupling between the secondary windings 12 and 13 the peakvoltage across the secondary winding 13 follows the voltage across thesecondary winding 12 to its low value. Therefore, the potential storedby the capacitor 35, or 55 volts, is greater than this low value and istherefore effective to back bias the diodes 33 and 34 whereby thesecondary winding 13 is completely unloaded or is effectively in an opencircuit condition. This, then, transfers the entire input energy fromthe primary winding 15 to the secondary winding 12, and, therefore, theentire output of the power supply is utilized to drive the electricaldischarge between the electrodes 25 and 26 and consequently the primarywinding 32 of the pulse transformer 31. With this circuit arrangement,this high frequency starting power is approximately an order ofmagnitude greater than that needed to start the commercially availablecompact-mercury vapor arc lamps under normal conditions and consequentlythe circuit of the present invention is capable of starting even agedlamps in one-half cycle of the power line voltage.

vAs was mentioned hereinabove, the circuit components are proportionedand defined in terms of a power frequency of 60 cycles and, therefore,the high radio or megacycle frequencies generated by the electricaldischarge between the electrodes 25 and 26 are presented with very lowirnpedances at these frequencies whereby the high frequency componentsin the electrical discharge are effectively placed directly across theprimary winding 32. In addition, the capacitor 35 and the secondarywinding 36 present a low impedance to these high frequency startingpulses whereby the starting pulse is applied directly between the anodeand cathode of the arc lamp to initiate the energization thereof.

With the initiation of current flowing between the electrodes of the arclamp the charge stored on the capacitor 35 is discharged through thelamp 14 whereby it is reduced to a level that unblocks the diodes 33 and34 and allows them to conduct. The charge stored on the capacitor 35rapidly drops to this unblocking potential, in this instanceapporximately 50 volts. With the conduction of the diodes 33 and 34, thepower from the primary winding 15 is switched back to the secondarywinding 13 and the starting circuit is essentially switched off sincethe voltage necessary for producing another electrical discharge betweenthe electrodes 25 and 26 cannot be reached with the winding 13unblocked. Therefore, the entire power from the primary winding 15 iscoupled to the secondary winding 13. After the lamp 14 begins to conductcurrent the voltage across the capacitor 35 and, therefore, across thelamp 14 drops automatically to a value which is approximately one-halfthe open circuit value for the lamp and which open circuit value issufiicient. to sustain the current flow through the lamp and maintain itener-- gized. The lamp, therefore, will remain energized under thesecircuit conditions as long as the power is maintained across the primarywinding 15.

It should also be noted that an important aspect of the present powersupply circuit is that after the lamp 14 is energized, if the power linevoltage should suddenly drop below the sustaining voltage for the lampandthe lamp becomes extinguished, the above automatic starting andswitching cycle will be rapidly and automatically initiated upon thereturn of the power voltage to its normal value. The lamp 14 would thenbe automatically ignited within 17 milliseconds of the application ofthe normal power to the circuit. This automatic starting feature is avery important feature, particularly when the invention is utilized inconjunction with arc lamps for recording oscillographs wherein a onesecond loss of data could be very costly.

The above circuit description is typical for a mercury lamp as utilizedin recording oscillographs. It is well known that xenon compact-arclamps'are employed in lieu thereof. The substitution of a xenon lamputilized with the present invention merely requires the opening of theswitch 38 to place the resistor 37 in circuit with the power circuit tothe lamp. Since the xenon arc lamp is typical of the lower power lamps,the resistor 37 is merely proportioned to be compatible with the ratedlamp power. The circuit operation, then, is identical to that describedhereinabove.

Now referring to FIGS. 3 and 4 another embodiment of the power supplycircuit of the present invention will be described. In general, thecircuit shown in FIG. 3 is essentially the same as the circuit of FIG.'1 in operation but has been modified to maximize the circuit operation.

As was indicated hereinabove, compact-arc lamps generally have aconstant power characteristic and, therefore, the ballast impedance musthave a voltage versus current characteristic to maintain the powerabsorbed by the lamp substantially constant over its operating range.Therefore, the voltage versus current characteristic curve is in theform of .a hyperbQla. To achieve this hyperbolic characteristic thereactive elements of the power transformer 11 have been modified wherebythe primary winding 15 is defined in terms of a pair of parallelinductors, shown in the drawings as the inductors 15A and 15B andcoacting with a pair of parallel inductors 13A and 13B. As will benoted, each of the inductors 15A and 15B are shown as having a pair ofwinding portions A-1 and A-2 and B1 and B-2. The portions A-1 and B-1are connected in parallel circuit relationship with the series inductor16. The other portions A-2 and B2 are connected in parallel and, inturn, this same parallel combination is connected in series with theresonating capacitor 17. This latter combination defines the circuitthat is resonant to the power line frequency. i

A further characteristic of this modified power transformer 11 is thatthe combination of inductors 13A and 13B are each defined to have adifferent impedance characteristic whereby the combination of theseimpedance characteristics approaches the desired hyperboliccharacteristic, at least over the normal operating range of the lamp andallows the lamp to function as a constant power device. These centertapped windings 13A and 13B have their center taps connected to ground,and each Winding has individual full wave rectifying elements 33A and34A and 33B and 34B individually connected thereto. These rectifyingelements are operated in parallel circuit fashion and are connected incommon to the power end of the filter capacitor 35.

The power circuit proper for the lamp 14 has also been modified wherebyan additional filtering element is utilized along with the filteringcapacitor 35 and which filtering element is shown as an inductor 41connected in series circuit with the output of the rectifiers 33 and 34and the secondary winding 36 for the pulse transformer 31. In addition,to aid the coupling of the starting pulse from the secondary winding 36to the lamp 14, additional capacitors shown as the parallel combinationof the capacitors 42 and 43 are coupled to the opposite terminal of thesecondary winding 36 from the arc lamp 14 and in parallel circuitrelationship therewith as shown. To this end, the filter capacitor 35may be onthe order of 2500 microfarads while the capacitors 42 and 43may be relatively small and on the order of 10 and .005 microfaradsrespectively. This latter pair of capacitors, then, reduce the impedanceto the starting pulse and aid in coupling the starting pulse to the lamp14.

The magnetic configuration of the modified power transformer 11 is shownin FIG. 4 with the corresponding windings of FIG. 3 identified byidentical reference numerals. It will be seen that the power transformercomprises a pair of rectangular magnetic core elements having three legswith the central leg in each instance defining the magnetic shunt andhaving an air gap G therein. As in the previous embodiment, the centralleg functions as the magnetic shunt whereby a substantial portion of theflux from the primary winding 15 is not coupled to the secondarywindings 12 and 13 to define the desired leakage reactance for lampballast purposes.

In addition, the starting circuit, including the secondary winding 12,has been modified through the inclusion of a, resonating capacitor 40connected in series circuit relationship between the secondary winding12 and the primary winding 32 for the pulse transformer 31. Thecapacitor 40 is proportioned relative to the inductance of the primarywinding 32 to resonate at the particular radio or microwave frequencywhich is necessary for starting the lamp 14 and preferably is physicallylocated adjacent the primary winding 32 to maximize the transfer of thestarting pulse. It will be recalled that a wide range of frequencies aregenerated due to the electrical discharge beween the pair of electrodes25 and 26 and, therefore, this combination of reactances tunes thestarting circuit to only the desired radio or microwave frequencieswhereby only these frequencies are essentially coupled to the arc lamp14 and, therefore, the transfer of energy at these frequencies isfurther maximized.

It should now be evident that the present invention provides animproved, simple, and inexpensive power supply that incorporates anautomatic lamp starting circuit therein.

What is claimed is:

1. A power supply for an arc lamp comprising a power transformer havinga ferromagnetic saturable core including a magnetic shunt with a primarywinding and at least a pair of secondary windings megnetically coupledthereto on opposite sides of the magnetic shunt, said transformerincluding means for producing asubstantially constant voltage in thesecondary windings, first circuit means connected to one of thesecondary windings and being responsive to energization of the primarywinding for generating an arc lamp starting pulse, and second circuitmeans connected to the other secondary winding for supplying an arc lampafter it is started, means included in the first circuit means coupledwith means included in the second circuit means for delivering thestarting pulse to the lamp supplying circuit, said second circuit meansincluding temporary storage means responsive to energization of theprimary winding for storing a preselected amount of energy therein tomomentarily place said other secondary winding in an open circuitcondition to transfer the input energy to said one secondary windingcausing the starting pulse to be generated and then releasing the storedenergy and transferring the input energy to said other secondary windingfor continuously supplying an arc lamp.

2. A power supply as defined in claim 1 wherein said means for producinga substantially constant voltage comprises a ferroresonant circuitdefined with the saturable core.

3. A power supply as defined in claim 2 wherein at least a portion ofthe primary winding is included in a circuit resonant to a powerfrequency to define the ferroresonant circuit.

4. A power supply as defined in claim 1 wherein said power transformeris further characterized by an excessive leakage reactance to functionas a lamp ballast.

5. A power supply as defined in claim 1 wherein said second circuitmeans includes rectifiers connected between the other secondary windingand the temporary storage device whereby the energy stored in saiddevice is effective to block the conduction of the rectifiers fortransferring the primary winding energy to said first circuit means forgenerating the starting pulse.

6. A power supply as defined in claim 1 wherein said first circuit meansincludes a pair of spaced electrodes adapted to generate an arc lampstarting pulse and Wherein said means coupling the first and secondcircuit means comprises a pulse transformer.

7. A power supply as defined in claim 1 wherein the power transformerhas a saturable magnetic core defined with at least three legs and aprimary winding and a plurality of secondary windings magneticallycoupled thereto, said primary winding being coupled to one of winding bythe third leg whereby the third leg acts as a magnetic shunt forproviding a fiux leakage path and thereby a leakage reactance, theleakage reactance being defined to function as a lamp ballast impedanceto cause the lamp to operate as a constant power device.

8. A power supply circuit for an arc lamp as defined in claim 7 whereinthe power transformer comprises a pair of saturable ferromagnetic coresfor defining a pair of inductors comprising the primary windings of saidpower transformer, said pair of inductors having diiferent impedancecharacteristics defined to cause the combination of the impedance valuesto approach a hyperbolic characteristic to allow a lamp to function as aconstant power device.

9. A power supply as defined in claim 1 wherein said temporary storagemeans comprises a capacitor.

10. A power supply circuit for an arc lamp comprising a powertransformer having a saturable magnetic core defined with at least threelegs and a primary winding and a plurality of secondary windingsmagnetically coupled thereto, said primary winding being coupled to oneof the legs and said secondary windings being coupled to another of saidlegs and being spaced from the primary winding by the third leg wherebythe third leg acts as a magnetic shunt defined for providing a fluxleakage path and thereby a leakage reactance, the third leg and therebythe leakage reactance being defined to function as a lamp ballastimpedance to cause the lamp to operate as a constant power device, acapacitor electrically connected to the primary winding to define aferroresonant circuit therewith to cause a constant voltage to begenerated in the secondary windings, a pair of spaced electrodeselectrically connected in circuit relationship with one of the secondarywindings to be energized therefrom, the electrodes being spaced apreselected distance for generating a lamp starting pulse, a pulsetransformer having a primary winding electrically connected in circuitwith said one secondary winding, and a capacitor electrically connectedto the other secondary winding to be energized therefrom, said othersecondary winding being effective to power a lamp after it is started,the secondary winding of the pulse transformer being connected to saidother secondary winding and adapted to be connected to a lamp to beenergized.

References Cited by the Examiner UNITED STATES PATENTS 2,509,188 5/ 1950Feinberg. 2,664,541 12/ 1953 Henderson. 2,757,318 7/ 1956 Noel.2,777,973 1/1957 Steele 315173 2,825,005 2/1958 Bird 315-289 3,036,2405/ 1962 Scott 315289 JOHN W. HUCKERT, Primary Examiner.

J. D. KALLAM, Assistant Examiner.

1. A POWER SUPPLY FOR AN ARC LAMP COMPRISING A POWER TRANSFORMER HAVINGA FERROMAGNETIC SATURABLE CORE INCLUDING A MAGNETIC SHUNT WITH A PRIMARYWINDING AND AT LEAST A PAIR OF SECOND WINDINGS MEGNETICALLY COUPLEDTHERETO AN OPPOSITE SIDES OF THE MAGNETIC SHUNT, SAID TRANSFORMERINCLUDING MEANS FOR PRODUCING A SUBSTANTIALLY CONSTANT VOLTAGE IN THESECONDARY WINDINGS, FIRST CIRCUIT MEANS CONNECTED TO ONE OF THESECONDARY WINDINGS AND BEING RESPONSIVE TO ENERGIZATION OF THE PRIMARYWINDING FOR GENERATING AN ARC LAMP STARTING PULSE, AND SECOND CIRCUITMEANS CONNECTED TO THE OTHER SECONDARY WINDING FOR SUPPLYING AN ARC LAMPAFTER IT IS STARTED, MEANS INCLUDED IN THE FIRST CIRCUIT MEANS COUPLEDWITH MEANS INCLUDED IN THE SECOND CIRCUIT MEANS FOR DELIVERING THE